1. Field of the Invention
The present invention relates to a scanning optical system having an ability to correct light beam deflecting surfaces which are not parallel or which lie in an irregular condition.
2. Description of the Prior Art
Various scanning optical systems for scanning a medium with a light beam are well known in the art. It is also known that the deflecting surfaces of a light deflector for deflecting the light beam in such a scanning optical system tend to be nonparallel or irregular, causing main scanning lines produced by the scanning optical system to be spaced at varying pitches or intervals. One proposal to this solution has been to use an elongated cylindrical lens for correcting the deflecting surface which is not parallel or which is irregular (see Japanese Laid-Open Patent Publication No. 50-93720).
However, the elongated cylinderical lens is not easy to manufacture, and hence a scanning optical system employing such elongated cylindrical lens is highly costly.
Where the angle of deflection of a light beam is large, the curvature of field produced by a focusing or image-formation system must be sufficiently corrected in both main scanning and subscanning directions in order to obtain a high-density beam spot diameter.